1. Field of the Invention
The present invention relates to display apparatuses to be used as steering auxiliary data source of vehicles for a driver, and more particularly to a vehicle display apparatus wherein image display is performed in superimpose of vehicle data, position data of vehicle or the like on video signals taking surroundings of the vehicle. The invention can be used in an apparatus installed in automobiles wherein a dead angle at surroundings of a vehicle is image-displayed, detection data of various sensors such as distance data between a vehicle and an obstacle and between a vehicle and a man are image-displayed in superimpose, or at ordinary running state various supervisory data of the vehicle are image-displayed in superimpose.
2. Prior Art
In a display apparatus of the prior art, when decomposition scanning is performed by an image pickup means such as television camera to perform photoelectric conversion, horizontal synchronizing signal and vertical synchronizing signal are overlaid on video signals, and composite scanning is performed by a CRT (cathode-ray tube) for display using the synchronizing signals, and at the composite scanning of the video signals obtained by the image pickup means, the video signals transmitted from an image memory circuit storing video signals such as pattern display, graphic display, character display are superposed. The video signals transmitted from the image memory circuit are superposed with the synchronizing signals when the display signals are read from the image memory circuit, and synchronous lead-in is performed so that the synchronizing signals of the image memory circuit is coincident with the synchronizing signal of the video signal, and then mixing of both video signals are performed.
That is, in the display apparatus of the prior art, the synchronizing signal of the video signal obtained by the image pickup means and the synchronizing signal of the video signal transmitted from the image memory circuit are caught at an image receiver side, and both are led in synchronizing state, and the video signal transmitted from the image memory circuit is superposed on the video signal obtained by the image pickup means.
In such display apparatus of the prior art, since both the image pickup means and the image memory circuit are provided with video synchronizing signal generating circuit, in order that such display apparatus of the prior art is made compact to be installed in vehicle bodies, there exists a problem.
Further, in automobiles, since possibility is high in invasion of noise in wide frequency range from medium frequency band up to UHF band by an ignition circuit, a flasher, a wiper, a horn or the like, if the video signal and the pattern signal have synchronizing signals independently, noise overlaid on one signal causes disturbance in synchronization and viewing of the display screen becomes difficult in the image display.